Year	constant 2021 PPP $ per kg of oil equivalent
1990	7.034704654231461
1991	6.9082760696447245
1992	7.024229991505478
1993	7.126132820074337
1994	7.277459728559781
1995	7.363501023036983
1996	7.60810312161899
1997	7.603681367591664
1998	7.83377597532989
1999	7.984475606697011
2000	8.102437109593088
2001	8.328495120970192
2002	8.402453437668074
2003	8.760701726382923
2004	8.959589034138167
2005	9.284505004350722
2006	9.513506391101169
2007	9.666388969136701
2008	9.591537581825342
2009	9.436178770876133
2010	9.715200215831247
2011	9.831361367907496
2012	9.914345420543203
2013	10.28393075867424
2014	10.40264950410894